JP4151014B2 - Isolated switching DC / DC converter - Google Patents

Description

  The present invention relates to a switching power supply device, and more particularly to a technique for realizing high efficiency and miniaturization of an insulating switching DC / DC converter.

  Conventionally, a boost half bridge (BHB) type switching power supply circuit in which a booster circuit and a half bridge circuit are integrated has been proposed (see Patent Document 1, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3). . A circuit configuration diagram proposed in Non-Patent Document 2 is shown in FIG. In FIG. 29, E is an input voltage source, L1 is an input choke coil, L2 is an output choke coil, Co is an output smoothing capacitor, Ro is a load resistance, and Vo is an output DC voltage.

  According to the BHB circuit shown in the figure, the input voltage source E is connected to the midpoint of two switch elements (FET1, FET2) in the half bridge configuration via the input choke coil L1, and the secondary of the transformer T The winding current is full-wave rectified by two synchronous rectification MOSs (FET3, FET4). The two switch elements (FET1, FET2) are configured to be controlled complementarily.

According to Non-Patent Document 3, a configuration is proposed in which a boost choke is taken into a primary winding of a transformer in the BHB method.
JP-A-11-262263 Haruo Watanabe, 2 others, “BHB (Boost Half Brigde) system power supply”, IEICE Technical Report, IEICE, EE98-17 (1998-07), p28-34 Haruo Watanabe, “High-efficiency on-board power supply by Boost Half Brigde”, 2000 Switching Power Supply System Symposium, Japan Management Association, B2-2 Yoshiaki Matsuda, “Low Voltage Output High Efficiency DC / DC Converter”, 2001 Switching Power Supply System Symposium, Japan Management Association, A2-3

  However, in the conventionally proposed circuit configuration, the output ripple voltage and ripple current are small, but the total DC bias of the core of the magnetic component (input choke coil, output choke coil, transformer) becomes very large. There are disadvantages in that the volume of the core is large and the efficiency of the entire apparatus is poor.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a switching DC / DC converter that can reduce the core volume and core loss of a magnetic component and can improve the efficiency of the entire apparatus. And

In order to achieve the above object, according to the present invention, a DC voltage source is connected to the primary side of an isolation transformer, and both the first switch element and the second switch element connected to the primary side are simultaneously connected. In an isolated switching DC / DC converter that performs voltage conversion by alternately turning on and off so as not to be in an on state, and obtains a DC voltage output via the secondary side rectifier circuit of the insulation transformer, the insulation transformer includes: The secondary side is a center tap type transformer, and the input choke coil, the primary coil of the insulating transformer, the secondary coil of the insulating transformer, and the output choke coil are wound around a common core, and The DC magnetic fluxes generated by the windings of these coils are configured to cancel each other, and the primary side of the insulating transformer is connected to the DC current. A series circuit of the input choke coil and the first switch element is connected between the terminals of the source, and a series circuit of the first capacitor and the primary coil is connected between the terminals of the first switch element. Rutotomoni, the first of the between the terminals of the switch element and the second switching element and Ri series circuit which are connected to the second capacitor, the number of turns of said input choke coil and the insulation transformer primary coil A primary side circuit of 2N (N is a natural number) is formed, and the secondary side of the isolation transformer is connected to the portion of the first secondary coil divided by the center tap of the secondary coil. The first rectifying element, the second rectifying element connected to the second secondary coil portion, and the output choke coil through which the current rectified by the first and second rectifying elements flows. And before It is seen containing an output smoothing capacitor connected to an output choke coil, wherein the first secondary coil and the number of turns of the second secondary coil, wherein in both the number of turns of the output choke coil n (n is a natural number) A secondary circuit is formed.

  According to the present invention, in a DC / DC converter using a center tap type insulation transformer on the secondary side, the input choke coil and the output choke coil are integrated with the insulation transformer, and the primary coil of the transformer is integrated in the same core (magnetic core). By winding the secondary coil and the input / output choke coil and designing the number of turns and the winding direction in the direction to cancel the DC magnetic flux created by each coil, the amount of DC bias of the core is made extremely small. . As a result, the volume of the core can be significantly reduced as compared with the conventional case, and the core loss can be reduced, so that a highly efficient device can be realized.

  As another aspect of the present invention, the connection location of the series circuit of the second capacitor and the second switch element in the primary circuit is changed, and the positive terminal of the DC voltage source and the negative terminal of the input choke coil There is also an aspect in which a series circuit of a second capacitor and the second switch element is connected between the terminal and a primary circuit having a configuration in which the input choke coil is connected in parallel.

  In the secondary circuit, the center tap is connected to the ground, and the output choke coil is connected to the first rectifying element and the second rectifying element. There is a mode in which an output choke coil is connected to the center tap.

  Furthermore, instead of the above-described center tap type insulation transformer, an aspect using a composite transformer having a first secondary coil and a second secondary coil on the secondary side is also possible.

  In this case, the input choke coil, the primary coil of the insulating transformer, the first secondary coil, the second secondary coil, and the output choke coil are wound around a common core, and The DC magnetic flux generated by these coil windings is configured to cancel each other, and the input choke coil and the first switch are connected between the terminals of the DC voltage source on the primary side of the insulation transformer. And a series circuit of a first capacitor and the primary coil is connected between the terminals of the first switch element, and the first circuit is connected between the terminals of the first switch element. A primary circuit is formed by connecting a series circuit of two switch elements and a second capacitor, and a first side connected to the first secondary coil is formed on the secondary side of the isolation transformer. Rectification element A second rectifying element connected to the second secondary coil, the output choke coil through which the current rectified by the first and second rectifying elements flows, and the output choke coil A secondary circuit including the output smoothing capacitor is formed.

  The connection location of the series circuit of the second capacitor and the second switch element in the primary side circuit configured using the composite transformer is changed, and the positive terminal of the DC voltage source and the negative terminal of the input choke coil There is also an aspect in which a series circuit of a second capacitor and the second switch element is connected between the terminal and a primary circuit having a configuration in which the input choke coil is connected in parallel.

  According to the present invention, in an insulation type switching DC / DC converter using a center tap system or a composite transformer in which a plurality of coils are provided on the secondary side of the transformer, the input choke coil and the output choke coil are integrated with the insulation transformer. Because the primary coil, secondary coil and input / output choke coil of the transformer are wound around the same core, and the DC magnetic flux of the core is made very small by canceling the DC magnetic flux generated by each coil. As compared with the conventional case, the core volume can be significantly reduced, the core loss can be reduced, and high efficiency of the apparatus can be achieved.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a circuit diagram of a DC / DC converter (step-up active clamp half-bridge converter) according to an embodiment of the present invention. In FIG. 1, Vi is an input power source, Lr1 is a leakage inductance, L1 is an input choke coil (number of turns 2N, N is a natural number), Q1 and Q1 'are switching elements using FETs, C1 is a DC component removing capacitor, C2 is a clamp capacitor, Lr2 is a leakage inductance, Tr is a center tap type isolation transformer on the secondary side (primary coil turns 2N, secondary coil turns n and n, n is a natural number), Q2 and Q2 'are synchronous rectifiers A switching element that functions as an element, Lr3 is a leakage inductance or the sum of an external insertion inductance and a leakage inductance, L3 is an output choke coil (number of turns n), Co is an output smoothing capacitor, and Vo is an output DC voltage. In this example, MOSFETs are used as the switching elements Q1, Q1 ', Q2, Q2', but other semiconductor elements may be used in the practice of the present invention.

  The input / output choke coils L1 and L3 are integrated with the transformer Tr, and the primary and secondary coils of the input / output choke coils L1 and L3 and the transformer Tr are wound around a common core (for example, EI type core). In other words, the DC magnetic fluxes generated by the windings of the respective coils are configured to cancel each other.

  FIG. 2 shows an example using an EI type core. As shown in the figure, the EI core 20 has a structure in which an E core 21 and an I core 22 are combined. A gap 23 is provided on the connection surface between the three magnetic legs 21 </ b> A, 21 </ b> B, 21 </ b> C of the E-shaped core 21 and the I-shaped core 22.

  As shown in FIG. 2, an input choke coil L1, a primary coil (2N) and a secondary coil (n, n) of a transformer Tr are wound around one outer magnetic leg 21A of the E-shaped core 21. An output choke coil L3 having n turns is wound around 21B. The right outer magnetic leg 21C in FIG. 2 is a magnetic leakage leg into which leakage magnetic flux flows.

  The direction of winding of each coil wound around the outer magnetic leg 21A and the central magnetic leg 21B is generated in each coil when a current flows through each winding, as indicated by a dot (·) in the figure. Magnetomotive forces are in a direction to cancel each other. In this way, by configuring a plurality of windings in a direction that cancels the DC magnetic flux, the amount of DC bias of the core can be made extremely small.

  Thus, the volume of the entire core can be significantly reduced, and the core loss can be reduced and the efficiency of the entire apparatus can be improved. In the implementation of the present invention, the shape of the core is not limited to the EI type core, and it is possible to use a core having another shape such as an EE type core.

  Next, the operation of the circuit shown in FIG. 1 will be described.

  FIG. 3 is an operation waveform of each part of the circuit shown in FIG. In FIG. 3, the periods other than mode 1 and mode 6 are shown longer than actual.

  In FIG. 3, VGS (Q1) and VGS (Q1 ') are the gate voltages of the switch elements Q1 and Q1', respectively. These two switching elements Q1 and Q1 'are alternately turned on / off by a control circuit (not shown) so that one of the two switching elements Q1 and Q1' is turned off while the other is turned on except for the periods of the dead times Td1 and Td2. The output DC voltage Vo can be controlled by changing the ratio of the ON period (ON duty ratio D) to the operating period Ts of the switch elements Q1 and Q1 '. That is, the output DC voltage Vo satisfies the relationship of the following equation.

[Equation 1]
Vo = (n / N) x D x Vi
VDS (Q1) in FIG. 3 is a waveform of the drain-source voltage of the switch element Q1. ID (Q1) is the sum of currents flowing through the switch element Q1, the body diode D1, and the output junction capacitor C11. ID (Q1 ') is the sum of currents flowing through the switch element Q1', the body diode D1 ', and the output junction capacitor C12. ID (Q2) is a sum of currents flowing through the switching element Q2 and the body diode D2. ID (Q2 ′) is the sum of currents flowing through the switching element Q2 ′ and the body diode D2 ′.

  The DC / DC converter circuit of this example can be divided into nine operating states of modes 1-9. The operation will be outlined with reference to an equivalent circuit corresponding to each mode. 4 to 12 are equivalent circuits of the modes 1 to 9. FIG.

[1] Mode 1; t0 ≤ t ≤ t1
In the mode 1 period, as shown in FIG. 4, the switch elements Q1 and Q2 are on, and the switch element Q1 has a current flowing from the input voltage source Vi through the input choke coil L1 and 1 of the transformer Tr. The next current is flowing. In FIG. 4, RL represents a load resistance, and Lm represents an exciting inductance of the transformer Tr.

[2] Mode 2; t1 ≤ t ≤ t2
After the switching element Q1 is turned off at t = t1, as shown in FIG. 5, the charging of the output junction capacitor C11 of the switching element Q1 by the current of the input choke coil L1 and the primary current of the transformer Tr, and the switching element Q1 The output junction capacitance C12 'is discharged. Along with this, the drain-source voltage of the switch element Q1 gradually increases, and at the same time, the drain-source voltage of the switch element Q1 'gradually decreases, and the winding voltage of the transformer Tr decreases. Incidentally, the gate signal of the switch element Q2 is normally turned off in this mode 2.

[3] Mode 3; t2 ≤ t ≤ t3
When each winding voltage of the transformer Tr becomes zero at t = t2, as shown in FIG. 6, the body diode D2 'of the switch element Q2' is turned on, and the winding of the transformer Tr is short-circuited. The current of the output choke coil L3 initially flows through the body diode D2 of the switch element Q2, but it gradually commutates to the body diode D2 'on the switch element Q2' side.

[4] Mode 4; t3 ≤ t ≤ t4
During the period of mode 4, after the body diode D1 'of the switch element Q1' is forward-biased and turned on at t = t3 as shown in FIG. 7, the current flowing through the body diode D2 becomes zero at t = t4. Is the period.

[5] Mode 5; t4 ≤ t ≤ t5
The period of mode 5 is a period from when the body diode D2 is turned off at t = t4 to when the gate signal of the switch element Q1 'is turned on at t = t5. In this mode 5, an ON signal is given to the gate of the switch element Q2 ′, and the switch element Q2 ′ is turned ON. At t = t4, the winding of the transformer Tr is released from the short-circuit state, and a winding voltage is generated.

[6] Mode 6; t5 ≤ t ≤ t6
The period of mode 6 is a period from when the gate signal of the switch element Q1 'is turned on at t = t5 to when the switch element Q1' is turned off at t = t6. During this time, the current direction of the switch element Q1 ′ changes from negative (in the direction of the dotted arrow in FIG. 9) to positive (in the direction of the solid arrow in FIG. 9).

[7] Mode 7; t6 ≤ t ≤ t7
During the period of mode 7, after the switch element Q1 'is turned off at t = t6 as shown in FIG. 10, the drain-source voltage of the switch element Q1 gradually decreases, and each winding voltage of the transformer Tr decreases. This is the period until it becomes zero at t = t7. Usually, in this mode 7, the gate signal of the switch element Q2 'is turned off.

[8] Mode 8; t7 ≤ t ≤ t8
When the winding voltage of the transformer Tr becomes zero at t = t7, the body diode D2 of the switch element Q2 is turned on as shown in FIG. 11, and the windings of the transformer Tr are short-circuited. The current of the output choke coil L3 initially flowed through the body diode D2 ', but gradually commutates to the body diode D2. Further, during this period, the drain-source voltage of the switching element Q1 continues to decrease further.

[9] Mode 9; t8≤t≤t9
Mode 9 is a period from when the body diode D1 of the switch element Q1 is forward-biased and turned on at t = t8 to when the body diode D2 'of the switch element Q2' is turned off at t = t9 (FIG. 12). Further, at t = t9, the winding of the transformer Tr is released from the short-circuit state, and a winding voltage is generated. During this time, the current direction of the switch element Q1 changes from negative (in the direction of the dotted arrow in FIG. 12) to positive (in the direction of the solid arrow in FIG. 12). After this mode 9 is completed, the mode 1 is restored.

  According to the switching DC / DC converter according to the above-described embodiment of the present invention, the input choke coil L1, the output choke coil L3, and the transformer Tr are integrated so that the magnetic flux generated by each winding is canceled out. Since the core is made very small, the core can be greatly reduced in size and the core loss can be greatly reduced as compared with the conventional circuit configuration. Thereby, the efficiency of the entire apparatus can be dramatically improved.

  The application range of the present invention is not limited to the circuit configuration shown in FIG. 1, and various modifications are possible. 13 to 28 show circuit modifications. For each circuit, the main differences from the circuit of FIG. 1 are pointed out, and the description of the circuit operation is omitted.

  The circuit shown in FIG. 13 is different from the circuit shown in FIG. 1 in the connection location of the series circuit of the capacitor C2 and the switch element Q1 ′. Other configurations are the same as those of the circuit of FIG.

  The circuit shown in FIG. 14 is different from the circuit of FIG. 1 in the connection location of the capacitor C1.

  The circuit shown in FIG. 15 is different from the circuit of FIG. 1 in the connection place of the series circuit of the capacitor C2 and the switch element Q1 'and the connection place of the capacitor C1.

  The circuit shown in FIG. 16 is different from the circuit of FIG. 1 in that the connection relationship between the capacitor C2 and the switch element Q1 ′ is switched.

  In the circuit shown in FIG. 17, the connection location of the capacitor C1 is further changed from FIG.

  In the circuit shown in FIG. 18, the configuration of the primary circuit of the transformer Tr is the same as that of FIG. 1, and the output choke coil L3 is connected to the center tap of the transformer Tr in the secondary circuit.

  The circuit shown in FIG. 19 employs the same configuration as that of FIG. 13 for the primary side circuit of the transformer Tr and the same configuration as that of FIG. 18 for the secondary side circuit.

  The circuit shown in FIG. 20 adopts the same configuration as that of FIG. 14 for the primary side circuit of the transformer Tr and adopts the same configuration as that of FIG. 18 for the secondary side circuit.

  The circuit shown in FIG. 21 adopts the same configuration as that of FIG. 15 for the primary side circuit of the transformer Tr and adopts the same configuration as that of FIG. 18 for the secondary side circuit.

  The circuit shown in FIG. 22 employs the same configuration as that of FIG. 16 for the primary side circuit of the transformer Tr and the same configuration as that of FIG. 18 for the secondary side circuit.

  The circuit shown in FIG. 23 employs the same configuration as that of FIG. 17 for the primary side circuit of the transformer Tr and the same configuration as that of FIG. 18 for the secondary side circuit.

  In addition, as the secondary circuit of the transformer Tr, the configuration shown in FIGS. 24 to 26 is possible. The circuit configuration shown in any one of FIGS. 1 and 13 to 17 can be used for the primary circuit of the transformer, which is omitted in FIGS. 24 and 25, respectively.

  In the example of FIGS. 24 and 25, the secondary side is replaced by the center tap type transformer Tr, and the secondary side has a first secondary coil having n turns and a second secondary coil having n turns separately. A wound composite transformer is used.

  Further, the circuit configuration shown in any one of FIGS. 18 to 23 can be used for the primary side circuit of the transformer Tr which is omitted in FIG.

  In the circuit examples of FIGS. 25 and 26, the switching elements Q2 and Q2 ′ are each driven at the gate terminal by the drain-source voltage of the other element.

  FIG. 27 and FIG. 28 show another modification regarding the primary side circuit of the transformer Tr. 27 and 28, the secondary side circuit of the transformer Tr is not shown, but the secondary side circuit omitted in these drawings may be any of those illustrated in FIGS. 1, 18, 24 to 26, etc. The circuit configuration can be used.

  In the circuit shown in FIG. 27, the connection location of the capacitor C1 is changed from the primary side circuit of FIG. That is, in FIG. 27, a series circuit of the primary coil of the transformer Tr and the capacitor C1 is connected between the terminals of the switch element Q1, and the switch element Q1 ', the capacitor C2, and the capacitor C1 are connected between the terminals of the switch element. The series circuit and the capacitor C1 are connected in series.

  The circuit shown in FIG. 28 differs from the primary circuit in FIG. 23 in that the connection location of the capacitor C1 is changed.

  The present invention is particularly useful in the case of a wide range, a high input voltage, a large capacity, and a low output voltage (for example, an input voltage of DC 200 to 400 V, an output of 15 V), such as for vehicles such as electric vehicles and hybrid vehicles. Of course, the scope of application of the present invention is not limited to this, and the present invention can be applied to power supplies of various uses and specifications.

1 is a circuit diagram of a DC / DC converter according to a first embodiment of the present invention. The figure which shows the example which utilizes EI type core The figure which shows the operation waveform of each part of the circuit shown in FIG. Equivalent circuit diagram showing operation of mode 1 in the DC / DC converter of this example Equivalent circuit diagram showing operation of mode 2 in DC / DC converter of this example Equivalent circuit diagram showing operation of mode 3 in DC / DC converter of this example Equivalent circuit diagram showing operation of mode 4 in DC / DC converter of this example Equivalent circuit diagram showing operation of mode 5 in DC / DC converter of this example Equivalent circuit diagram showing operation of mode 6 in the DC / DC converter of this example Equivalent circuit diagram showing operation of mode 7 in DC / DC converter of this example Equivalent circuit diagram showing operation of mode 8 in the DC / DC converter of this example Equivalent circuit diagram showing operation of mode 9 in DC / DC converter of this example The circuit diagram which shows the 2nd Embodiment of this invention Circuit diagram showing a third embodiment of the present invention Circuit diagram showing a fourth embodiment of the present invention Circuit diagram showing a fifth embodiment of the present invention Circuit diagram showing a sixth embodiment of the present invention Circuit diagram showing a seventh embodiment of the present invention Circuit diagram showing an eighth embodiment of the present invention Circuit diagram showing a ninth embodiment of the present invention Circuit diagram showing a tenth embodiment of the present invention The circuit diagram which shows the 11th Embodiment of this invention Circuit diagram showing a twelfth embodiment of the present invention Circuit diagram showing a thirteenth embodiment of the present invention Circuit diagram showing a fourteenth embodiment of the present invention A circuit diagram showing a fifteenth embodiment of the present invention. Circuit diagram showing a sixteenth embodiment of the present invention. Circuit diagram showing a seventeenth embodiment of the present invention Circuit diagram of conventional BHB system DC / DC converter

Explanation of symbols

  Vi ... input power supply, L1 ... input choke coil, Q1, Q1 '... switch element, C1 ... DC component removing capacitor, C2 ... clamp capacitor, Tr ... transformer, Q2, Q2' ... switch element, L3 ... output choke coil, Co: Output smoothing capacitor, 20: EI type core

Claims (6)

A DC voltage source is connected to the primary side of the isolation transformer, and the first switch element and the second switch element connected to the primary side are alternately turned on / off so that they are not simultaneously turned on. In the insulation type switching DC / DC converter that performs voltage conversion and obtains a DC voltage output through the secondary side rectifier circuit of the insulation transformer,
The isolation transformer is a center tap type transformer on the secondary side, and the input choke coil, the primary coil of the isolation transformer, the secondary coil of the isolation transformer, and the output choke coil are wound around a common core. And the direct-current magnetic flux generated by the windings of these coils cancels each other,
On the primary side of the isolation transformer, a series circuit of the input choke coil and the first switch element is connected between the terminals of the DC voltage source, and a first circuit is connected between the terminals of the first switch element. with a series circuit of the capacitor and the primary coil are connected, Ri series circuit formed is connected between the first and the second switching element and a second capacitor between the terminals of the switch elements, the input A primary side circuit in which the number of turns of the choke coil and the primary coil of the insulation transformer is 2N (N is a natural number) is formed,
On the secondary side of the isolation transformer, a first rectifying element connected to a portion of the first secondary coil divided by a center tap of the secondary coil, and a portion of the second secondary coil A second rectifying element connected to the output choke coil, the output choke coil through which the current rectified by the first and second rectifying elements flows, and an output smoothing capacitor connected to the output choke coil. In addition, a secondary circuit is formed in which the number of turns of the first secondary coil and the second secondary coil and the number of turns of the output choke coil are both n (n is a natural number). Isolated switching DC / DC converter. A DC voltage source is connected to the primary side of the isolation transformer, and the first switch element and the second switch element connected to the primary side are alternately turned on / off so that they are not simultaneously turned on. In an isolated switching DC / DC converter that performs voltage conversion by obtaining a DC voltage output via the secondary-side rectifier circuit of the isolation transformer,
The isolation transformer is a center tap type transformer on the secondary side, and the input choke coil, the primary coil of the isolation transformer, the secondary coil of the isolation transformer, and the output choke coil are wound around a common core. And the direct current magnetic flux generated by each of these coil windings is configured to cancel each other,
On the primary side of the isolation transformer, a series circuit of the input choke coil and the first switch element is connected between the terminals of the DC voltage source, and a first circuit is connected between the terminals of the first switch element. A series circuit of a capacitor and the primary coil is connected, and a series circuit of a second capacitor and the second switch element is connected between the positive terminal of the DC voltage source and the negative terminal of the input choke coil. There Ri formed are connected in parallel with the input choke coil, number of turns of said input choke coil and the insulation transformer primary coil (N is a natural number) together 2N formed the primary side circuit is,
On the secondary side of the isolation transformer, a first rectifying element connected to a portion of the first secondary coil divided by a center tap of the secondary coil, and a portion of the second secondary coil A second rectifying element connected to the output choke coil, the output choke coil through which the current rectified by the first and second rectifying elements flows, and an output smoothing capacitor connected to the output choke coil. In addition, a secondary circuit is formed in which the number of turns of the first secondary coil and the second secondary coil and the number of turns of the output choke coil are both n (n is a natural number). Isolated switching DC / DC converter.   3. The isolated switching DC according to claim 1, wherein the center tap is connected to a ground, and the output choke coil is connected to the first rectifying element and the second rectifying element. / DC converter.   The insulated switching DC / DC converter according to claim 1, wherein the output choke coil is connected to the center tap. A DC voltage source is connected to the primary side of the isolation transformer, and the first switch element and the second switch element connected to the primary side are alternately turned on / off so that they are not simultaneously turned on. In the insulation type switching DC / DC converter that performs voltage conversion and obtains a DC voltage output through the secondary side rectifier circuit of the insulation transformer,
The insulation transformer is a composite transformer having a first secondary coil and a second secondary coil on the secondary side, an input choke coil, a primary coil of the insulation transformer, and the first secondary coil. And the second secondary coil and the output choke coil are wound around a common core, and the direct-current magnetic flux generated by these coil windings is configured to cancel each other.
On the primary side of the isolation transformer, a series circuit of the input choke coil and the first switch element is connected between the terminals of the DC voltage source, and a first circuit is connected between the terminals of the first switch element. with a series circuit of the capacitor and the primary coil are connected, Ri series circuit which are connected between the first and the second switching element and a second capacitor between the terminals of the switch elements, the input A primary side circuit in which the number of turns of the choke coil and the primary coil of the insulation transformer is 2N (N is a natural number) is formed,
On the secondary side of the isolation transformer, a first rectifying element connected to the first secondary coil, a second rectifying element connected to the second secondary coil, and the first a 1 and the output choke coil rectified current flows through the second rectifier element, and an output smoothing capacitor connected to said output choke coils, only contains the first secondary coil and the second An insulated switching DC / DC converter , wherein a secondary circuit is formed in which the number of turns of the secondary coil and the number of turns of the output choke coil are both n (n is a natural number) . A DC voltage source is connected to the primary side of the isolation transformer, and the first switch element and the second switch element connected to the primary side are alternately turned on / off so that they are not simultaneously turned on. In the insulation type switching DC / DC converter that performs voltage conversion and obtains a DC voltage output through the secondary side rectifier circuit of the insulation transformer,
The insulation transformer is a composite transformer having a first secondary coil and a second secondary coil on the secondary side, an input choke coil, a primary coil of the insulation transformer, and the first secondary coil. The coil, the second secondary coil, and the output choke coil are wound around a common core, and the direct-current magnetic flux generated by the windings of these coils is configured to cancel each other.
On the primary side of the isolation transformer, a series circuit of the input choke coil and the first switch element is connected between the terminals of the DC voltage source, and a first circuit is connected between the terminals of the first switch element. A series circuit of a capacitor and the primary coil is connected, and a series circuit of a second capacitor and the second switch element is connected between the positive terminal of the DC voltage source and the negative terminal of the input choke coil. There Ri formed are connected in parallel with the input choke coil, number of turns of said input choke coil and the insulation transformer primary coil (N is a natural number) together 2N formed the primary side circuit is,
On the secondary side of the isolation transformer, a first rectifying element connected to the first secondary coil, a second rectifying element connected to the second secondary coil, and the first a 1 and the output choke coil rectified current flows through the second rectifier element, and an output smoothing capacitor connected to said output choke coils, only contains the first secondary coil and the second An insulated switching DC / DC converter , wherein a secondary circuit is formed in which the number of turns of the secondary coil and the number of turns of the output choke coil are both n (n is a natural number) .

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